Who can I contact when I think that the air carrier breached his obligations and I want to lodge a complaint?

Each Member State is obliged to designate an appropriate body to enforce Regulation No 261/2004 on its territory.

A list of these bodies is available here. Competencies of the supervisory authorities differ in every country. These authorities are not always competent to make decisions in particular disputes between carriers and passengers. Usually, the authorities have the right to apply financial sanctions in case of detected violations.